Control information for electronic devices of an analog nature is commonly achieved by the use of a rotary or linear potentiometer. By adjusting such a device, an analog signal such as an audio signal can be directly affected by the potentiometer and thereby attenuated or amplified as a function of the position of the potentiometer. Control of other parameters or non audio signals can be accomplished by using the potentiometer to vary a DC voltage or current which interfaces to some controlling circuitry. With the acceptance and proliferation of digital systems it has become necessary to input control signals in a digital manner. While it is possible to convert an analog voltage from a potentiometer to a digital signal which can be interpreted by digital controller, this method can be costly and limited.
A simple method for sending control information to a digital system can be accomplished by the use of a momentary push switch. Commonly, two such push switches have been used to allow a user of an automotive radio system, for example, to increase or decrease the volume. Pushing the up switch once would increase the volume by a predetermined amount while holding the switch will ramp the volume up at a given rate. The same would apply for the volume down switch. Switches are sometimes seen as undesirable for use as audio controls and many manufacturers have opted to use a rotary encoder in order to transfer the user input to the control circuit. A typical rotary encoder has two internal contacts arranged in a quadrature configuration. As the shaft is rotated, the switches make and break consecutively. Use of a quadrature decoder circuit or software algorithm can then be used to determine the direction and rate of rotation.
A conventional rotary switch mechanism has certain aspects of its construction which can make it a less desirable input device for digital control information. The construction of such a mechanical encoder tends to be costly, requiring very small and precise switch contacts and rotary mechanism. In addition, because it is a mechanical device, it is subject to wear and the effects of the environment. The conventional through shaft design makes it difficult to seal the switch chamber against the elements.